[T3] a stumper!

[Jon Stiles]

Keith,

This certainly sounds like a radio interference issue. I have had similar problems crop up in customer cars in a few scenarios that may be present. So here is an exhaustive “maybe” list:

Using non-resistor style spark plugs with L-Jet and D-Jet

One faulty spark plug with an internal or unseen manufacturing defect

Using aftermarket non-resisted spark plug leads.

Using a non-resisted rotor.

A rotor that sits too high on the distributor shaft and a distributor shaft that has too much vertical play. (Common when using a Compufire points replacement). As the engine spins up, the shaft will want to rise up and will just kiss the plastic moulding on the cap, usually on a post that has a little extra casting plastic left over. This would be rare as I have only seen that twice in 25 years.

Having an external relay (that powers anything) near the FI trigger wire from the distributor to the computer module, or near the hall sensor wires.

A faulty Temp 2 sensor (L-Jet)

A stuck vacuum advance plate

On bad or worn injector in which its solenoid is not able to fire at a continuous rpm range. (I check them by sound with a 9 volt battery wired to an injector plug with a button switch. They should all sound the same, if one has a softer click it may be the culprit.)

With that list the most common is spark plug, leads, rotor, or lead connector radio interference.

Hope this can help. Intermittent RPM dependent miss-firing can be super frustrating.

Jon Stiles



> On May 17, 2021, at 9:24 AM, Keith Park <topnotch at nycap.rr.com> wrote:
> 
> They are a set of reset points, but I do have another set you did to try,
> Grasping for straws really looking for that one bad connection that would
> cause an RPM 
> Reliant issue and cant think of one.
> 
> Keith
> 
> 
> Topnotch Restorations
> topnotch at nycap.rr.com
> http://www.topnotchresto.com
> 71 Squareback  “Hothe”
> 65 Notchback  “El Baja Rojo”
> 93 RX7  “Redstur”
> 13 Subaru Outback "Blendin"
> 
> -----Original Message-----
> From: type3-vwtype3.org <type3-vwtype3.org-bounces at lists.vwtype3.org> On
> Behalf Of Jim Adney
> Sent: Monday, May 17, 2021 10:02 AM
> To: type3 at vwtype3.org
> Subject: Re: [T3] a stumper!
> 
>> On 16 May 2021 at 20:14, Keith Park wrote:
>> 
>> Any thoughts about the trigger points also having an issue like this? 
> 
> I don't think it's likely, but I suppose it's possible. Do you have a
> different set of points you could try?
> 
> Old trigger points need to be "reset" as the rubbing blocks wear down. It's
> important to make sure that cam is free of rust and dirt, to minimize wear
> and it should have a thin layer of sticky grease on it to lube the rubbing
> block.
> 
> I reset the trigger points on every distributor I rebuild. I can also just
> reset trigger points rather cheaply if you send them to me. ISTR that I
> reset several of Keith's a few years ago.
> 
> I've certainly seen problems that were caused by trigger points worn out of
> spec, but I don't recall those problems being RPM related.
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
> 
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